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12 volt coils on a 55


KAD36
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Been going through ignition coils pretty quick lately, like 3 in the past 2 years, all with different failures.  Summary:

 

BVD brand oil filled - lasted 1 year, left me stranded.  Started cutting out at hot until car wouldn’t start at all. Ever. Didn’t measure the impedance.  Got so mad I threw it in the woods behind the house.

 

Blue Streak oil filled - lasted almost a year.  This was also on the second rebuild and with a newly rebuilt 56 distributor, so new condenser, rotor etc.  Engine cuts out when hot.  runs fine when cold.  Meets primary and secondary impedance spec at cold, open secondary hot. 

 

NAPA Echlin UC12 oil filled - lasted about 2 weeks.  Almost left me stranded.  Car had weak spark ran at fast idle only.  Started sputtering at idle.  Secondary opened up to 120K ohms all temperatures.  Measured 7.5K ohms when it was working.

 

In each case, I went back to my trusty Blue Streak High Energy HD epoxy filled Made in the USA because its says so stamped on the bottom coil from 1983 that has fired this car for over 60,000 miles and man does that thing make a freakin intimidating blue spark at the plug.  1.4 ohms on the primary and 10.1K ohms on the secondary.  Either that or the original Delco that was on the car from the mid 60s still works good - 1.5 on the primary, 8K on the secondary.  That Delco one might be tar filled, not sure, but it doesn’t slosh around.  The only reason I am wanting to replace the coil is preventative maintenance and having a new coil might be smarter than driving around with a 35+ year old coil, rather keep it as a road kit spare.  Huh - imagine that.

 

The coil wire is good at .32 ohms non suppression wire, the ballast is good at 1.8 ohms, the dwell is 27 deg, the plug gaps are all good at .035, and based on math I would anticipate the primary voltage is in the high 5 to low 6 volt range, not enough to overwhelm the secondary and cause them to overheat, the condensers, rotors and other distributor components have all been swapped by swapping out the 55 distributor with a 56 distributor to match the new 56 engine so even the resistor in the rotor was technically exchanged.  A simple check on both condensers was done to make sure they were not breaking down when hot.  

 

I cannot seem to find a common mode failure other than some articles that suggest that todays not made in the USA oil filled coils do not survive well horizontally, even if the terminals are rotated to the 3 and 9 o’clock positions to keep the coils cooler and immersed in the oil.  

 

My research also suggested if you need to mount a coil horizontally, get the epoxy filled one, they can be mounted in any orientation, they will not short out over time and are made for higher vibration.   Huh?? Yet I see some folks mounting oil filled coils horizontally and zero issues. The original coil, per the shop manual, say they were oil filled.  

 

Perhaps the newer primary/secondary mountings in the oil filled design are not as robust to vibration mounted horizontally as the old ones?

 

Anyone have any experience in this epoxy vs oil filled part or could suggest something else to check - or a brand thats been recently working well for them? They sort of all look like the same made in China ones - the Pertronix flamethrower and Accel look a little different.

 

I will go out soon and measure the voltage on the primary when its running but don’t expect it to be wildly off from my calculations.

 

BTW NAPA advertises an epoxy filled coil for an extra 20 bucks but when you buy it guess what, its not epoxy filled its oil filled.  Same 3 yr 36000 mile warranty as the UC12 oil filled.  Joe counter dude told me I was paying 20 bucks for “more quality.”  “See mister, you’re getting more quality”.  Really?  Where - the paint?  They were the same coil with the same markings with the same warranty with a 20 dollar price difference! “Oh yeah - good eye mister”  

 

Say - hold this wire for me, this is how more quality is supposed to work.  Grrrrr.

 

Worst case, I’ll buy a name brand epoxy coil and run it just to see what the heck happens because now I’m really curious what’s going on.  Thanks for any input.

 

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Posted (edited)
3 hours ago, Ben Bruce aka First Born said:

Been running a Pertronix for 12 years, 20,000 + miles.  No points. Color me happy.

 

  Ben

Thanks Ben - good to hear from you - is that a separate cylindrical coil and mounted which way?

 

Thanks Chris - I almost got the Standard but went with the blue streak because I thought it was Standards better product.  Am wondering if these days that may not be the case.  I considered a Delco but it looks like all the other China junk.  Perhaps it depends what shop overseas does the windings.  Lots of articles to read, some conflicting, some also experiencing low service life.  Seems to point to overseas vs on shore workmanship.  May have to call to get specifics.  Post 34 and last 3 paragraphs of post 40 in a simple format sums up all  I’ve read so far:

 

https://www.jalopyjournal.com/forum/threads/mounting-a-coil-sideways-yes-or-not-recommended.688224/page-2

 

My intent really is to ensure there isn’t another gremlin someplace else in the car that I may overlooking - and don’t want to ruin the old coils.

Edited by KAD36 (see edit history)
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Spark plug wires:  resistance?  wire core?  continuity from terminals inside cap to the plug connection?....any added resistance in the system puts a bigger load on the coil.  Turn on your AM radio in the garage with the antenna down and off a station to check the characteristics of the static.

Is there a way to measure the resistance of resistor plugs?...some may be different.  (I run Autolite 85 with good results; the non resistor Autolite 75 is a good choice as long as there are no sensitive electronics like a cruise control)  Platinum and other exotic electrode plugs are for fuel injected car with higher voltage electronic ignition (apparently take more voltage to fire and if fouled will not recover).

  Run a dependable working coil...old or new!

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Posted (edited)

I was reading and thinking along the line of Old Tank. An oscilloscope or a secondary voltage inductive pickup should narrow it down. Most 12v points cars run around 3000 to 3500 volts on the secondary side. Check each cylinder. See if they are all high or just  one or two. You have the electrical resistance as well as the fuel mixture at the gap as contributors to the load.

 

Just a thought, do your batteries seem short lived? Maybe your primary voltage is unstable.

 

Presented with the same problem Albert Einstein would probably say "Look somewhere else". There's a quote he made.

 

 

Edited by 60FlatTop (see edit history)
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All good points Willie thanks -

 

- non suppression solid core wires - soldered at the ends.  I only measured the resistance of the coil wire because it was common path to all the other wires I can spot check the other wires.  I did visually inspect the wires when I rebuilt it and the ends were all intact.  Suppression wires would have higher resistance.

 

- non resistor plugs. Only resistor in the system is in the rotor, same as factory set up. Suppose I could go to resistor plugs.  The Autolites you recommended to me are in the old 55 heads.

 

- no “ticking” on AM radio, staticky though but thats been a consistent behavior since like forever

 

- Cap has brass inserts - I have an NOS stock of the older ones that I use, same as points.  suppose I could pull the cap leave the wires on and ring it out to each plug.  Seems there would be a miss or a hitch at idle, and this thing idles like a swiss watch.

 

-  NOW - something you did just key me onto is what might the variation of resistance on the carbon block be that is on the rotor.  From the book:

 

Radio Suppressor and Capacitor. A 10,000 ohm resistor is built into the distributor rotor so that it is unnecessary to install a suppressor on the high tension cable when a radio is installed. A capacitor is mounted on the side of 1955 Buick ignition coil and connected to the positive (battery) terminal of coil when a radio is installed.

 

Most of the articles on reliable, horizontally mounted oil filled coils are 7-15 years old.  My suspicious is that was when there were still ones made in the US that had more consistent workmanship than the overseas ones of today.

 

 

 

 

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18 minutes ago, 60FlatTop said:

 Check each cylinder. See if they are all high or just  one or two.

 

Just a thought, do your batteries seem short lived? Maybe your primary voltage is unstable.

 

 

 

Hi Bernie - been getting about 5+ years out of NAPA batteries, they seem good.  I have the idle up a bit so they don’t discharge.  

 

That’s 2 votes to go ring out all the wires.  Yay. :D 

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53 minutes ago, KAD36 said:

 NOW - something you did just key me onto is what might the variation of resistance on the carbon block be that is on the rotor.  From the book:

 

Radio Suppressor and Capacitor. A 10,000 ohm resistor is built into the distributor rotor so that it is unnecessary to install a suppressor on the high tension cable when a radio is installed. A capacitor is mounted on the side of 1955 Buick ignition coil and connected to the positive (battery) terminal of coil when a radio is installed.

Measure your collection of rotors so I don't have to ;)...inquiring minds want to know.

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50 minutes ago, old-tank said:

Measure your collection of rotors so I don't have to ;)...inquiring minds want to know.

 

You just love giving out work assignments don’t you LOL

 

Will check the voltage drop across the resistor Chris.

 

 

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4 hours ago, KAD36 said:

You just love giving out work assignments don’t you LOL

And helping spend money and drinking their beer.

I checked 3 rotors, one new and two used.  All had open circuits.  The two used showed signs of heating at the ends of the carbon rod area.:o

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21 minutes ago, old-tank said:

And helping spend money and drinking their beer.

I checked 3 rotors, one new and two used.  All had open circuits.  The two used showed signs of heating at the ends of the carbon rod area.:o

 

I’m gettin there Texas I’m getting there…. :)  Am busy doing a whole lot of nothing and just left NAPA with a corp rep. Apparently a population of the IC676s are marked wrong.  He will be getting back with me in next day or so.  This is gettin good.

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Posted (edited)

The two on the left were purchased within the past 2 years.  They measure .5 and .6 ohms.  Like a dead short.  The .6 ohm one is in the car.

 

The two on the RIGHT are older ones - the 12.7 K ohm one is very old and out of the 55 distributor with many miies on it but still works ok.  The 143K one is new and never installed.  These two were purchased probably 10 years ago.  You can see the carbon resistor is almost potted in the newer ones and inserted in the two older ones.  These are all standard motor parts.

 

The spec says 10K ohms.

 

Hmmm my hip shot reaction is run resistor plugs if using the zero ohm rotors and solid non suppressor wires because the secondary is probably pumping out a lot of current with the low impedance rotor…. Wonder what other brands for rotors measure?  More to come…..

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Edited by KAD36 (see edit history)
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Posted (edited)

You know this reminds me of the engine fiasco.  The spec tolerance was exceeded on individual parts but when connected as a system the error budgets all happened to fall within total system spec.
 

If in the day there were non resistor plugs and solid wires in these cars and the rotor carried the system secondary resistance of 10K would that suggest the secondary current to the plugs was 2.5 - 4 amps assuming the secondary plug voltage was 25000 - 40000 volts? Even with no resistance in the rotor, and running newer resistor plugs and suppression wires I bet the typical resistance of any one line from coil to plug would be in the 15-25k ohm range which would put the current in the 1-3 amp range?

 

Translation: at idle with less than 12 volts feeding the ballast resistor and hence the primary, I bet my 143k ohm rotor if used would limit current and produce a really weak spark being 10x higher resistance than found in a typical system, and the .5 ohm dead short rotors when not using resistor plugs or suppression wires were probably what fried that Napa coils secondary in 2 weeks with too high a current.  And the 55 correct impedance rotor was on the prior “newer” blue streak coil and that coil just broke after almost a year - not due to electrical overload - but due to current day workmanship standards and being oil filled and mounted on its side.  Where the older oil filled coils (or present day epoxy) can better tolerate horizontal on engine mounting as evidenced as coming from the factory that way.

 

That’s the current hypothesis.   More to come.  Go ahead, start shooting.
 

Edited by KAD36
Get my facts straight (see edit history)
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In 57 the 10k resistor was taken out of the distributor rotor.  Who has a 57 knows where that secondary ignition resistance went - if anywhere.?  Were resistor plugs or wires specified?  What do you run?

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You really need to measure the secondary voltage to each plug while the engine is running. Ohms law works but there are other factors. A lean mixture from the carb can raise all the voltages. An air leak on one runner will show up as higher voltage.

 

If you are a person who maintains the car buy doing various tests with the coil wire pulled, some do a compression test like that, you can be overtaxing your coil during those tests possibly causing a premature failure of the coil.

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Posted (edited)
6 hours ago, 60FlatTop said:

You really need to measure the secondary voltage to each plug while the engine is running. Ohms law works but there are other factors. A lean mixture from the carb can raise all the voltages. An air leak on one runner will show up as higher voltage.

 

 

Fair point Bernie - you are right there are other factors to consider and that’s beyond my math. Not having a way to measure the plug voltages my thought was a rough order of magnitude relationship and the KISS principle.  What do you think of a 150k ohm variation in the SAME parts?  That impedance seems like a clue since its 10x more than a resistor plug, which is on the order of 5K ohms plus 2 feet of resistor wires which would be on the order of 10k ohms.  Doesnt make sense to me why the resistance was eliminated in the new aftermarket rotors ( unless it was a tech oversight like the Napa epoxy coil) and if that could affect the coil reliability?

 

I have a 57 distributor set up but now am hesitant  to drop it in until this all makes a little more sense.  Maybe just pop in resistor plugs keep the rotor and let it go.  Don’t want to overthink it!

Edited by KAD36 (see edit history)
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Posted (edited)
21 hours ago, 60FlatTop said:

If you are a person who maintains the car buy doing various tests with the coil wire pulled, some do a compression test like that, you can be overtaxing your coil during those tests possibly causing a premature failure of the coil.

Not often no, however If by this you mean the coil wire arc jumps direct to the block during the tests that’s similar to how the Napa coil was configured for 2 weeks with no resistive element from coil secondary to rotor, cap, plug, block.  Interesting.

 

Update from the field: 

 

Key on, engine off, no crank, points closed:  batt 12.5; 5.4 volts across primary, 7 volts across ballast.

 

Engine idle: 13.5 batt, 3.5 across primary, 4 across ballast.  Not really pure DC when running but for those interested.

 

Wire measurements all 8 under 1 ohm.  .3 to .8 ohms measured from inside of cap brass lug to end of plug boot

 

143k ohm rotor produced a weak spark by eyeballing it. I tossed it and kept the 2 dead short ones.

 

Cleaned up the used 12k ohm rotor put that in and the resistor 85 auto lite plugs in with the old epoxy coil.  Smooth idle no high speed miss fires right up

 

The search for in spec spare parts continues 

 

 

Edited by KAD36 (see edit history)
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Just to leave a coil tip for future reference, to prevent possible damage to my ignition coil I always clip a wire from the coil wire to a good ground if I am doing a compression test or any service that requires cranking the engine with the secondary circuit disabled. it is the old Ohm's Law formula where I reduce R to a minimum, thereby reducing the coil output to almost zero. Pulling the coil wire and letting it dangle will create a high resistance air gap that will pull everything the coil has. That could blow your coil, adding to your problems or aggravate a failing condition. Best to ground it and be safe.

 

I have never owned one, but they used to make a coil capacity tester that would create a resistance equal to 120% of the coil design capacity. That is a safe operating test for a good coil. I can't recall many bad coils on cars I have serviced. Learning about grounding was something I leaned at least 40 years ago. Maybe it worked.

 

Just remember:

 

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Posted (edited)

Primary Ignition Resistance tolerances - Hemmings

 

Check out last 2 paragraphs which may help explain the situation.  

 

The problem that the automobile collector deals with today is out-of-specification ballast circuits that look correct but that have the wrong resistance or skew greatly under high heat load in the engine compartment. An ignition coil that has the wrong internal resistance often exacerbates this condition and leads to a poor-running engine for which you can find nothing wrong. 

 

Tried one more test today just because it was bugging me

 

Long story short, the Delco OEM original ballast was carefully disassembled completely and every metal to metal contact point polished until I got it down to solid 1.8 ohms, lowest it could get, about .25 ohms less than before.  Measured the whole primary circuit impedance and voltages and al values were as expected with no stray impedance that could unexpectedly drop the primary voltage.  Monitoring battery voltage when under hood temp was good and hot, both in N and D at idle with some electrical loads on/off and playing with the idle speed to dip the battery voltage, the engine used to sputter and die at about 12.5 volts unless I jumped across the ballast quick enough or turned off a big electrical load like the headlights or AC compressor and blower then it would smooth right back out.  Now with the lower ballast value after cleaning it just runs rough down to 12.03 volts but doesnt die. Also, coil primary impedance went up as expected from 1.4 ohms cold to 1.7 ohms hot, further aggravating the situation.  

 

So looking for a ballast closer to factory low end spec of 1.4 ohms. Alternative would be to improve charging at low rpm but not re-opening that can of worms with hit or miss mechanical regulators and playing the bend the tab game.

 

In my road kit I have a spare delco ballast thats 2 years old that is 2 ohms, also out of spec, so that would just make the problem even worse.  Have a couple parts coming into NAPA and will measure them Monday.

 

Edited by KAD36 (see edit history)
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Would effectively removing the ballast resistor help. I see on my car the coil and ignition wire are directly connected to each other on one side of the ballast resistor. Meaning the ballast resistor has no part to play other than be a point where the two wires connect.

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Posted (edited)

Yes it would help temporarily, I’d be concerned about point life long term because my coils primary is low resistance and it needs a current limiting (ballast) resistor on there while running.  Thats an interesting situation on your car - am assuming you have no issues with point life or cold starting?  Might the coil on your car have an internal primary resistance of 3 ohms or more instead of 1.5 ohms and doesn’t need an external resistor?  Incidentally 3 ohms is he total max resistance in the shop manual for the primary plus ballast!

 

When the charging system (generator and mechanical regulator) is good and hot (underhood - hood closed) with a mild electrical load at idle (like sitting at a long red light or a chain of red lights) it will dip down to 12.2-12.4 volts and thats where my problems seem to start - any stray losses rob voltage from the coil.  Just a few tenths of a volt higher at the battery and it totally goes away like the Dodge in the Hemmings article. Or if the hood is open so the regulator doesn’t get as hot, the problem is minimized.  Otherwise normal op voltage is around 13+ volts, 14.9 max cold, zero issues.  Seems as long as the primary always sees about 6 bolts or more there’s enough secondary voltage to fire the plugs.   I have 2 aftermarket regulators and a very old Delco junkyard one on the shelf and not one of those aftermarkets regulate even closely the same over temperature with a good battery - understanding charging rate is lowered as temperature goes up  - the one in the car now was the best of the bunch.  One of them actually discharged the battery when it got to normal operating temp at highway speeds with no electrical load, and that might be 10 miles down the road, but worked fine when cool and couldn’t be returned.  If a new reason is needed to drink a lot of beer try figuring out how to adjust mechanical regulators without blowing something up. Those spring mount tabs are way super touchy.  The original-original regulator busted (and also is on the shelf) and had adjustment screws, which are rare as hens teeth, to adjust the spring pressure.

Edited by KAD36 (see edit history)
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37 minutes ago, KAD36 said:

 If a new reason is needed to drink a lot of beer try figuring out how to adjust mechanical regulators without blowing something up

😄🤞

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10 hours ago, BuickRiv55 said:

Would effectively removing the ballast resistor help. I see on my car the coil and ignition wire are directly connected to each other on one side of the ballast resistor. Meaning the ballast resistor has no part to play other than be a point where the two wires connect.

I assume you have a 55 and with it wired that way the life of the points will be decreased significantly, unless you have electronic ignition like Pertronix.  Even then if using Pertronix it should be wired through the ballast resistor and a stock coil used since the hotter spark will overheat the carbon rod in the rotor and it will catch fire and burn!

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Back in the early 1950's even a lesser car like a Chevy would get diagnosed with an array of specialty tools and meters. Sometimes I am surprised at how condensed that tool kit is 70 years later. Well, maybe not that surprised.

445171803_ServiceTool.JPG.b6a7b3074351735275a37b583f8d49da.JPG

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Good point.  One thing appears consistent.  The guy on the right is overdue for a beer, hand on hip, customer being a PITA, Friday 430….

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  • 2 months later...
Posted (edited)

Thought to summarize my findings after all the word salad trying to figure out the stalling problem when hot … waited until there was about 600 miles before reporting out.  So far no misfire, stalling, shutdown or weak spark issues at hot even in the 95 deg heat.
 

coil: pertronix “verified epoxy filled” 1.5ohm primary.  Am not totally knocking the new aftermarket oil filled coils but this one fixed my run of bad luck with new oil filled coils mounted horizontally.  Carry a spare.

rotor: the .5 ohm one with no suppression resistance (out of spec but resistor plugs offer secondary impedance)

plugs: auto lite 85 resistor plugs (4K ohms each)

wires: solid core no resistance

regulator: aftermarket  

idle speed: 550-575 in D with AC off.  Add about 120 rpm during AC season (650-675).  Helps w charging and cooling at idle w AC on.

ballast resistor: modified aftermarket.  Trim about 2 coils off end to give 1.4 ohms vs 1.8-2 ohms.  It’s possible to fit the new wire element into the old ceramic housing I just haven’t done it yet.  The wire to the right of the meter is what was trimmed off to meet spec in the shop manual.

 

image.jpeg.3a0069c8eab6cadb59307aa5122dab04.jpeg

 

Hope this helps someone. Carry on 😎

Edited by KAD36 (see edit history)
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I’ve always been told not to Mount an oil filled coil horizontally as the top of the windings won’t be covered in oil and eventually it’ll cook itself.. I’ve been running an epoxy filled msd one for years with no problems in this New Mexico heat.. I’m also running a full msd set up as well.

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1 hour ago, 1956322 said:

I’ve always been told not to Mount an oil filled coil horizontally as the top of the windings won’t be covered in oil and eventually it’ll cook itself.. I’ve been running an epoxy filled msd one for years with no problems in this New Mexico heat.. I’m also running a full msd set up as well

 

Glad to know you heard something similar - thanks for posting - there were a couple threads on the tri-five Chevy and HAMB sites where guys were fighting this exact same coil mounting and infant mortality issue while others dug in stating they experienced no long term reliability issues.


The original 60 yr old Delco coil that was on the car from the 60s still works fine and I must have spun that “new” coil in all kinds of directions to cover the windings in oil and they still failed.  I did notice if I shake the original Delco coil when cold I can’t hear it slosh at all but when it’s hot there is a very faint liquid sound.  Makes me think they were filled with more oil and of higher viscosity back then but that’s my pure speculation.  Maybe the design needed less room to expand when hot and could tolerate less air space.  Maybe it was more structurally sound internally also.

 

We could probably all agree current offshore replacement parts are inferior to and have a wider variation in quality and acceptance standards as compared to the Made in the USA products found on our cars when in daily service.

 

For “more better” stories see post 33 and 40 in link below - about summed it up for me.  Stupid parts.

 

https://www.jalopyjournal.com/forum/threads/mounting-a-coil-sideways-yes-or-not-recommended.688224/page-2

 

 

 

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